So, is lead magnetic? Lead is diamagnetic in nature. The sole reason behind this is the alignment of atomic spins in the reverse direction to that of applied magnetic fields. Basically lead is a paramagnetic atom with 2 unpaired electrons (electronic configuration is [Xe] 4f14 sd10 6s2 6p2 ), but “lead metal” is diamagnetic because the unpaired electrons pair up in bonding MOs. Another reason is that the magnetic susceptibility of this diamagnetic metal is -1.8. Lead, with a symbol Pb (derived from the Latin word plumbum), has an atomic mass of 207.2 u and atomic number 82. It belongs to the post-transition metals and can be easily extracted from ores. Galena is the main ore of lead which also bears silver. Metallic lead beads were found in Asia Minor, back in 7000-6500 BC. The spike in the spread of lead production was due to its association with silver, obtained by burning galena. Now let’s move onto the reasons for lead’s magnetic properties in a more detailed way.
Why is Lead Diamagnetic?
Lead’s diamagnetism is because of its alignment of magnetic dipoles in the opposing direction to that of the applied magnetic field. Adding to this, magnetic susceptibility is also negative for this metal, indicating its repulsive nature from magnets. While paramagnetic or ferromagnetic materials are attracted to magnets, diamagnetic materials tend to repel the applied magnetic field. The applied magnetic field creates an induced magnetic field in the opposite direction, causing a repulsive force. As a Pb atom, with an electronic configuration of [Xe] 4f14 5d10 6s2 6p2 , have 2 unpaired electrons in p orbital. Thus it will remain as a ‘paramagnetic atom’. But in Pb metal, the unpaired metals will pair up in the bonding MO. and thus will be diamagnetic. Given below is the MO diagram of PbO, focusing on the Pb part we can understand the above-mentioned fact.
The green lines are the atomic orbitals of lead with 6s and 6p. Both have 2 electrons but in a paid fashion. Next, the blue line is the orbitals of the 6p having 2 electrons again in paired fashion. And if we look at the molecular orbital of PbO (light blue lines), there also, electrons are in a paired way. Thus this MOT depicts the diamagnetic nature of Pb. Below given is a video where the magnetic attraction is compared between aluminum, copper, brass, and lead.
In the video, the movement of the magnet is a lot quicker in lead than the rest. The reason for that is the difference in the electrical resistivity of these metals. The lower the electrical resistance, the higher is the current and stronger the magnetic field that’s produced. So, Lead has the highest resistance and thus shows the weakest magnetic field among the four metals.
Magnetic Susceptibility of Lead
According to different facts, it is clear that magnetic susceptibility is negative. The value is -1.8. This negative value indicates that the lead’s magnetic effect is repulsive in nature, i.e diamagnetic. Now magnetic susceptibility is a degree to which a metal can be magnetized in an external magnetic field. In simpler words, whether a particular metal will be attracted or repelled and in what amount, is determined by this factor. It is positive in the case of paramagnetic and ferromagnetic substances. Negative for diamagnetics and zero if the material does not respond to magnetic fields. Also with respect to Crystal Field Theory, we can see that the magnetic moment of lead is zero, due to the non-availability of unpaired electrons. Magnetic moment tells us about the magnetic strength of a metal. Hence it’s another proof that lead is diamagnetic. If you want to check its magnetic moment the formula is given below:-
Does lead block magnetic fields?
First of all, no metal can block magnetic fields. They can be re-routed around materials with high permeability. But lead has a permeability of 1. So it doesn’t have any effect on magnetic fields. Permeability is basically the quality or state of being permeable. In electromagnetism, it is the degree of magnetization that a material obtains in an applied magnetic field. If a material with high permeability is nearby, the magnetic field lines will travel the path of least resistance i.e through the high permeability material, rather than the magnetic field in the surrounding air. Thus lead with so low permeability, like that of air, will not reroute the magnetic fields in any way. Pure lead has a bright, silvery color with a tint of blue. Some of the characteristics that lead possess are high density, malleability, ductility, and high resistance to corrosion. This metal has a very low melting point compared to most metals, 327.5℃ (621.5℉). The boiling point i.e 1749℃ (3180℉) is also the lowest among the carbon group elements.
Why can Pb(+4) be reduced to Pb(+2) easily?
The pair of electrons in 6s orbitals remains chemically inert due to the inert pair effect. So Pb2+ attained a configuration with fulfilled d and f orbitals. Additionally, there is a very high positive value for E°pb4+/pb2+ indicating that Pb4+ has a higher tendency to get reduced into Pb2+. The oxidation state of +2 is more stable than +4 due to this inert pair effect. Actually, the inert pair effect is an application of the relativistic effect. Now the question becomes, what is the relativistic effect? So, basically in heavier elements relativistic variation of the mass of electrons becomes prominent to cause overall contraction of atoms. This contraction is known as relativistic contraction. Note that this effect is important for Z>80. In Pb, due to the relativistic effect of 6s, there is a very high promotional energy from 6s to 6p. This energy cannot be compensated by bond formation. Thus the electrons in 6s remain chemically inert. This will lead to a configuration like- [Xe] 4f14 5d10 6s2, which have fulfilled d and f orbital making Pb2+ more stable than Pb4+.
Properties of Lead (Pb)
This metal appears as blue-whitish and lustrous in nature. Like other metals, it is highly malleable, ductile in nature. At a temperature of 20°C, its density is around 11.34 g.cm-3. Its melting point is 327 °C and the boiling point is 1755 °C. It has its 13 isotopes that are also the end products of radioactive elements. Lead consumption can be very dangerous to health causing kidney damage, rise in Blood Pressure.
Conclusion
At the end of the article we can sum up that lead is a diamagnetic substance. The main reason for this is the alignment of magnetic dipoles in the opposite direction to that of the external magnetic field. Another reason is, that the electrons are in paired fashion in the MO diagram of Pb. Also, its magnetic susceptibility is negative indicating that lead repels from the external magnetic field.
